Means of conveying articles in clean rooms include ordinary conveyor belts with some of the moving parts shielded or covered with exhaust hoods to draw particles away, and expensive specialized robotic arms using exotic nonparticulating surfaces on moving parts that are subject to friction.
There are many types of conveyors. Roller conveyors use rotating wheels or cylinders to support the conveyed articles. These conveyors are typically stationary. A conveyor belt uses a flat or trough shaped endless belt cycling around pulleys at either end. Drag conveyors use a stationary tray or trough along which pushers or bars travel, dragging conveyed articles with them. Vibratory conveyors rapidly move upward and forward, then downward and backward, such that conveyed articles are thrown toward the discharge end in many tiny steps. Variations of these types use gravity or applied mechanical power in different ways.
A walking beam conveyor typically comprises two subassemblies of long bars or beams aligned parallel to the direction of conveyance. One subassembly, called the stationary beam, comprising at least two bars of equal length and height spaced side by side, supports the conveyed articles most of the time. A second subsassembly, called the walking beam, also comprising at least two bars of equal length and height spaced side by side relatively more closely than those of the stationary beam, is positioned in between the bars of the stationary beam. This second subassembly moves up between the bars of the stationary beam, lifting the conveyed article slightly above the stationary beam. The second subassembly then moves forward, advancing the article, and then lowers it again to the stationary beam. The second subassembly then moves down below the level of the stationary beam, where it is not touching the conveyed article, and moves back to its original starting position. The conveyed article advances along the conveyor in several steps, resting on the stationary beam between steps.
Walking beam conveyor assemblies are often utilized where article movement between discreet locations at long time intervals is desired, as on a slow production line with several work stations. Where uneven starting and stopping motion is undesirable, the walking beam drive mechanism may be modified with gear motors having gradual starting and stopping characteristics, or cranks which pause at the points in their travel where the tangential component of motion vanishes, or hydraulic cylinders having special flow controls, so as to make the required starting and stopping less jarring to the conveyed article.
Walking beam conveyors are sometimes applied to contamination sensitive applications, for example in food processing where lubricants and abraded metal particles from the mechanism must be prevented from contaminating the food articles being conveyed. The moving linkages required to support the walking beam and its motion are located beyond the used zone of the conveyor if article travel from one end of the conveyor to the other is not required and if special constructions are used. Sealed bearings and stainless steel mechanical parts may also be used. These measures are somewhat successful at reducing contamination, but with corresponding compromises in expense and utility.
There is a need for a conveyor system that can be used in clean room environments that is relatively inexpensive to construct and is easy to use without requiring special exhaust hoods and enclosures or expensive, exotic, low particulating surfaces and which provides more control over particulation.